[Java] Move ArrowBufPointer out of the java the memory package

The memory package is focused on memory access and management. ArrowBufPointer should be moved to algorithm package as it isn't core to the Arrow memory management primitives. I would further suggest that is an anti-pattern.

**Reporter**: [Jacques Nadeau](https://issues.apache.org/jira/browse/ARROW-7533) / @jacques-n
#### PRs and other links:
- [GitHub Pull Request apache/arrow#6208](https://github.com/apache/arrow/pull/6208)

_{**Note**: *This issue was originally created as [ARROW-7533](https://issues.apache.org/jira/browse/ARROW-7533). Please see the [migration documentation](https://github.com/apache/arrow/issues/14542) for further details.*}

Esamina prima la PR #6208, poi individua ArrowBufPointer e i suoi riferimenti nei package Java di memoria e algoritmi. Verifica che lo spostamento lasci coerenti i riferimenti e la struttura dei package, e verifica che il progetto continui a essere compilato correttamente.

Scritto dal modello di indicizzazione a partire dal testo della issue.